1. Field of the Invention
This invention relates generally to communication systems and, more particularly, to circuitry for providing electrostatic protection and impedance matching for radio frequency circuit components in integrated circuits.
2. Background of the Invention
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), wireless application protocols (WAP), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and share information over that channel. For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver receives RF signals, removes the RF carrier frequency from the RF signals via one or more intermediate frequency stages, and demodulates the signals in accordance with a particular wireless communication standard to recapture the transmitted data. The transmitter converts data into RF signals by modulating the data in accordance with the particular wireless communication standard and adds an RF carrier to the modulated data in one or more intermediate frequency stages to produce the RF signals.
As the demand for enhanced performance (e.g., reduced interference and/or noise, improved quality of service, compliance with multiple standards, increased broadband applications, et cetera), smaller sizes, lower power consumption, and reduced costs increases, wireless communication device engineers are faced with a very difficult design challenge to develop such a wireless communication device. Typically, an engineer is forced to compromise one or more of these demands to adequately meet the others.
Costs of manufacturing a radio frequency integrated circuit (IC) may be reduced by switching from one integrated circuit manufacturing process to another. For example, a CMOS process may be used instead of a bi-CMOS process since it is a more cost effective method of IC manufacture, but the CMOS process increases component mismatches, increases temperature related variations, and increases process variations.
Two problems commonly encountered in the design and manufacture of RF signal integrated circuits relate to impedance matching of various RF signal processing components and control of electrostatic discharges to prevent damage to components inside the integrated circuit. Proper impedance matching is important for an efficient transfer of signal and energy from a xe2x80x9csourcexe2x80x9d to a xe2x80x9cload.xe2x80x9d In an integrated circuit for processing RF signals, impedance matching is especially important to ensure an efficient transfer of an RF signal from the antenna to a receiver filter module or a low-noise amplifier.
Electrostatic discharges are well known as a major contributing factor in damaging integrated circuitsxe2x80x94both during the manufacturing process and during use of the circuit. Integrated Circuits often come into contact with accumulated static charge on surfaces such as the human body and assembly equipment. The voltage potential that accompanies such built up static charge is often on the order of Kilovolts. When accumulated static charge finds a discharge path through the pins of an integrated circuit, often through contact, electrostatic discharge occurs. These events can result in highly concentrated currents that cause severe heating in the physical circuit devices of an integrated circuit. Severe heating can cause permanent damage to these devices. Therefore, protective circuits or structures must be employed to prevent damage caused by electrostatic discharge. Electrostatic protection circuits must be capable of quickly and efficiently routing electrostatic discharge between any combination of pins of an integrated circuit, eliminating significant voltage differential and preventing damage to circuit devices.
Therefore, a need exists for circuit that can be optimized to provide both impedance matching and protection from the damaging effects of electrostatic discharges.
The electrostatic-discharge/impedance-matching circuit disclosed herein for use in radio frequency (RF) integrated circuits substantially meets these needs and others. The electrostatic-discharge/impedance-matching circuit of the present invention is broadly comprised of at least one shunt circuit operable to shunt current related to an over-voltage condition and at least one series element operably coupled to the shunt element. The shunt element and series element in combination provide electrostatic discharge protection for the RF signal processing circuit elements on the integrated circuit and also provide a matched input impedance for an incoming RF signal. Various alternate embodiments of the electrostatic-discharge/impedance-matching circuit include first and second shunt elements and a series element operably connected in combination to provide optimal electrostatic discharge protection and impedance matching.
The electrostatic-discharge/impedance-matching circuit can be placed at various locations on the integrated circuit to provide optimal performance depending on the particular architecture of the integrated circuit. In one embodiment, the electrostatic-discharge/impedance-matching circuit it located between a transmitter/receiver switch module and an antenna receiving incoming RF signals. In another embodiment, the electrostatic-discharge/impedance-matching switch is located directly between an antenna and a receiver filter module. In other embodiments, the electrostatic-discharge/impedance-matching circuit is located between a receiver filter module and a low-noise amplifier.
Other features and advantages of the present invention will become apparent from the following detailed description of the invention made with reference to the accompanying drawings.